NR2F6, known also as EAR-2, is an orphan nuclear receptor that was cloned in a search for homologues of the retroviral oncogene v-erbA using low stringency hybridization (see Miyajima, N., et al., (Identification of two novel members of erbA superfamily by molecular cloning: the gene products of the two are highly related to each other. Nucleic Acids Res, 16(23): p. 11057-74. 1988)). EAR-2 is a member of the chicken ovalbumin upstream promoter (COUP) family of nuclear receptors. The COUPs function in vitro as transcriptional repressors, antagonizing the activation ability of a wide range of nuclear receptors that play prominent roles in differentiation. Accordingly, aberrant expression of COUP-TFI inhibits retinoid-induced epithelial and neuronal differentiation in vitro (Please see Kyakumoto, S., M. Ota, and N. Sato (Inhibition of retinoic acid-inducible transcription by COUP-TFI in human salivary gland adenocarcinoma cell line HSG. Biochem Cell Biol, 77(6): p. 515-26. 1999), Neuman, K., et al., (Orphan receptor COUP-TF I antagonizes retinoic acid-induced neuronal differentiation. J Neurosci Res, 41(1): p. 39-48. 1995) and Adam, F., et al., (COUP-TFI (chicken ovalbumin upstream promoter-transcription factor I) regulates cell migration and axogenesis in differentiating P19 embryonal carcinoma cells. Mol Endocrinol, 14(12): p. 1918-33. 2000)). The roles of COUP-TFI and COUP-TFII in mammalian development have been studied by targeted deletion in the mouse. COUP-TFI deficient mice exhibit numerous defects in axonal development, including failure of development of the nucleus of the 9th cranial nerve. COUP-TFII deletion causes widespread defects in angiogenesis and cardiac development, leading to embryonic lethality in mid-gestation. Seven-up (svp), the Drosophila COUP family homologue, is also important in embryonic development; with null mutations of seven-up being embryonic lethal. svp is involved in decisions of cell fate determination during the development of the photoreceptors in the ommatidium of the eye and regulates proliferation during the development of the malpighian tubules by regulating the expression of cell cycle regulators. Improvements are needed in the field of screening test compounds to identify agonists and antagonists of the orphan nuclear receptor NR2F6.